(a) Field of the Invention
The present invention relates to a liquid crystal display, and a method of testing the liquid crystal display. More particularly, the present invention relates to a liquid crystal display and a method of testing the liquid crystal display which easily detects the formation of a bridge between sub-pixel electrodes as well as between data lines of the liquid crystal display.
(b) Description of the Related Art
A liquid crystal display (“LCD”), an extensively used flat panel display device, includes two display panels mounting field-generating electrodes such as pixel and common electrodes thereon, and a liquid crystal layer sandwiched between the electrodes. The LCD generates an electric field in the liquid crystal layer by applying voltages to the field-generating electrodes, and aligns the liquid crystal molecules within the liquid crystal layer to control the polarization of light incident thereto, thereby displaying desired images.
Various tests should be made to detect defects of line breaks or short-circuits in fabricating the LCD, such as an open short (“OS”) test, an array test, a visual inspection (“VI”) test, a gross test, and a module test.
When source and drain electrodes are separated from each other during the process of fabricating a thin film transistor (“TFT”) on a first panel in the LCD, the OS test is made to detect a break of the signal lines or a short-circuit of the TFT by applying a predetermined voltage thereto. Before the mother glass is divided into a plurality of cells, the array test is made to detect a break of the display signal lines by applying a predetermined voltage thereto and identifying the presence or absence of the output voltage. After the mother glass is divided into the plurality of cells and the upper and lower panels are assembled with each other, the VI test is made to visually detect a break of the display signal lines by applying a predetermined voltage thereto. Before the driving circuit is mounted, the gross test is made to detect the display image quality and a break of the display signal lines by applying the same voltage as the practical driving voltage thereto and identifying the display screen state. After the driving circuit is mounted, the module test is made to finally detect the optimal operation of the driving circuit.
A vertically-aligned (“VA”) mode LCD provides an LCD in which the directors of liquid crystal molecules are aligned vertical to the upper and lower panels with no application of an electric field, as this gives a high contrast ratio and a wide reference viewing angle. The reference viewing angle refers to a viewing angle with a contrast ratio of 1:10, or an inter-gray luminance inversion limit angle.
With the VA mode LCD, cutouts or protrusions may be formed on the field-generating electrodes to realize the wide viewing angle. As the direction of the liquid crystal molecules to be inclined is determined by way of the cutouts or protrusions, the inclination directions of the liquid crystal molecules can be diversified, thereby widening the reference viewing angle.
However, the VA mode LCD involves poor visibility at the lateral side thereof, compared to the visibility at the front side thereof. For example, with the case of a patterned vertically aligned (“PVA”) mode LCD having cutouts, the luminance thereof is heightened as it comes to the lateral side thereof, and in a serious case, the luminance difference between high grays is eradicated so that the display image may appear to be distorted.
In order to enhance the lateral side visibility, it has been proposed that each pixel should be divided into two sub-pixels, with the sub-pixels within each pixel receiving different voltages. However, when electrodes for the sub-pixels are patterned during the process of fabricating the LCD, a bridge may be formed such that it interconnects the sub-pixel electrodes or the neighboring data lines. From the circuit perspective, this means that those electrodes or data lines are short-circuited with each other. Consequently, the same voltage, rather than different voltages, is applied to the respective sub-pixels, thereby deteriorating the display image quality.